In the railway building sector two major applications can be identified:                providing the rail joints by means of drilled tie plates arranged on both sides of the drilled web of two adjacent rails and screwed by means of horizontal bolts, such as to form the continuous rail level. This application requires a horizontal screwing or unscrewing operation from the rail side in a narrow operating space due to the bulky presence of the ties and the ballast consisting of either pebble gravel or concrete.        The anchorage of the rail couplings to the ties is carried out by means of vertical screws. This application requires a vertical screwing or unscrewing operation from above.        
The mounting or dismounting of the truck wheels consists in screwing or unscrewing the wheel locking nuts while being in the horizontal position.
Since the above operations are niche applications, the tools known so far for carrying out these operations are substantially similar to motor-driven tools developed for other applications on a larger scale, such as the gun-handle wrenchs for use in the metal carpentry constructions and in the mass-produced mechanical constructions, bush-cutters and chain saws.
This entails drawbacks due to the dimensions and positioning of the wrench, the resulting reaction moment performed by the user, as well as the work posture which the latter is forced to take.
The one-hand handle of the gun-type is not suitable for the great moments required by railway applications.
The wrenchs manufactured based on bush-cutters have two separate handles, differently spaced apart from the motor axis and arranged such as to be staggered in the direction of the motor axis. This configuration, together with the bulk of the motor unit itself does not allow the horizontal use for making the rail joints. Furthermore, the mutual arrangement of the handles and their location relative to the motor axis entail that reaction moment performed by the user acts around an inclined axis relative to the motor axis and the “deviating” parts of the reaction moment cause a mispositioning of the tool and an unhealthy posture by the user.
The wrenchs manufactured based on chain saws have only one handle perpendicular to the motor axis and integrally formed in the plastic housing of the wrench also defining the tank. In some cases a further handle is provided, also perpendicular to the motor axis and staggered relative to the first handle along said motor axis. A wrench of this kind is described and illustrated in the German utility model G 88 05 367. With this configuration, the user is forced to work in an ergonomically incorrect position and the fixed gripping positions, i.e. of the hands, relative to the rotation axis, require a notable effort to resist to the screwing/unscrewing torque. In the case where the accelerator button (arranged in the first handle) is operated with the forefinger, the user's posture will be further worsened. On the contrary, by using the thumb to operate the accelerator button, the user's posture will be improved but the gripping capacity of his hand will be compromised.
Furthermore, the fact that both the handle and the tank are integrally formed in the plastic housing of the wrench limits on the one hand the volumetric capacity of the tank, and consequently the wrench autonomy of operation, and on the other hand it exposes the handle (which is fragile) to knocks and damages.
Therefore, the object of the present invention is to devise an impact motorized wrench with such characteristics as to overcome the drawbacks cited with reference to the prior art.